The present disclosure relates to rotary electric machines such as vehicle engine starter machines including electric motors, and particularly starter machines used in change of mind start-stop applications.
Recent requests by vehicle manufacturers for start-stop engine starter systems are specifying a warm start requirement for high speed operation in addition to the traditional cold start requirements of high torque, lower speed operation of the starter machine. A typical cold start (Conventional Start) condition is identified in the graph of FIG. 4 entitled “Start-Stop Starter Motor Enhancement.” Due to their occurrence at higher than usual cranking speeds, these warm start points, can be difficult to accommodate with traditional starter motor designs, which were intended to perform under cold start conditions. A typical warm start (Stop-Start) condition is identified in FIG. 4. Conventional and/or historical approaches to augment the output of the starter motor have included modifications providing flux weakening, winding pattern shifting, or even mechanical gear shifting, which add cost and/or complexity, and may compromise performance of the starter under cold start conditions. It is desirable to enhance performance of the starter motor in the starter machine's high speed region (or low torque region) in simpler, less costly ways.